The present invention relates to a wood chipper which includes a rotary chipper wheel, and a feed roller that will drive logs, branches and the like into the chipper wheel. The wheel and feed roller are driven by separate hydraulic motors, and the hydraulic circuit includes a flow priority valve that provides priority of flow to the chipper wheel motor, and includes a relief valve that is set so that the feed roller can be reversed if jams occur.
Various lock chippers have been advanced in the art, and problems with jamming the chipper wheel that is used have existed. For example, U.S. Pat. No. 3,524,485 shows a log chipping apparatus that has a rotatable chipping wheel and an infeed conveyor, with a speed sensing device for sensing changes in speed of rotation of the chipper wheel. The feeding conveyor is enabled or disabled in accordance with the changes in speed of the chipper wheel.
Drives for moving logs or pieces of wood into a chipping rotor that can be operated to retract the log either with the manual operation or at the time when the cutter speed drops below predetermined amount have been known, as shown in U.S. Pat. No. 4,598,745. This is sensitive to slowing of the chipper rotor or wheel, and reverses the drive of the log when the chipper wheel speed drops.